计算两个不同的SQL查询结果的比率，返回数字

如果你把这两个查询都作为CTE使用，那么它就变得相对简单了。

WITH q1
     AS (SELECT Count(DISTINCT user_id) total_daily_active_user_group_month
         FROM   (SELECT user_id,
                        Monthname(TIME) mon,
                        Count(*)        cnt
                 FROM   activities
                 WHERE Month(TIME) = Month(Now() - interval 1 month)
                 GROUP BY user_id,
                           Month(TIME))),
     AS (SELECT Count(DISTINCT user_id) total_daily_active_user_group_month
         FROM   (SELECT user_id,
                        Monthname(TIME) mon,
                        Count(*)        cnt
                 FROM   activities
                 WHERE Month(TIME) = Month(Now() - interval 1 month)
                 GROUP BY user_id,
                           Month(TIME)
                 HAVING cnt = 31))
SELECT q1.total_daily_active_user_group_month /
       q2.total_daily_active_user_group_month
       AS result
FROM   dual;  
你评论说，你得到一个错误，指向WITH关键字；切换到两个子查询，然后；简化。
select a.value / b.value as result
from (select count(distinct user_id) value
from ... your 1st query goes here